Last night, I experienced some really strange incident on 107.5 FM when in vertical position.
Between 2 AM and 2:30, I heard classical music on this frequency, suddenly becoming very strong.

The signal was not 100 % clear and the middle frequency was 107.550 MHz in stereo and with RDS.
However, the RDS signal was empty and program type /radiotext was not set.

Around 2:15, I heard the clear announcement by a lady this was supposed to be ARD Nachtkonzert.
As there is no "usual" station which carries this overnight programme on 107.5, I was confused.

After 2:30 the classical music was mixed by hiphop and The Voice which I heard before 2 was back.
My suggestion is that 107.5 Naestved gets its signal from 96.1 KBH which was swamped out by NDR Kultur.

I have a slight suspicion, that the signal might have come from 96.1 MHz Flensburg that was also strong this night.
What might be a hint is the fact that The Voice came along in stereo and with empty RDS since then.

Well, I think it would actually be very strange to feed such an important transmitter like Naestved this way.
Any other thoughts and ideas about the result are very appreciated but I think that`s the solution, weird enough.

Very strange, but conditions were extraordinary. I missed them, but Dutch DX''ers had danish DAB stations in full audio. I had a strange experience myself. During the huge opening to Spain/Portugal yesterday afternoon I had RDP Antena 2 Portugal on 88,7 on my carradio (whilst parked) . It prompted my carradio's automatic tuning (traffic patrol) to retune to Dutch radio 2. I tuned back manually to 88,7, had Antena 2 again but my radio retuned automatically to Dutch radio 2. Never experienced this before.

this is not surprising as both are using the same PI code 8202 (not even local) but of course, different PS and px. content
I have read about several coincidences , even if only one number (the 3rd??) is different .
the car radio regards both incoming signals as the same station, also when "REG" is turned off in that specific case
only "MANUAL" or "RDS-AF OFF" would prevent to switch

during the development of RDS_PI (and even earlier, ARI traffic information), planners thought about giving the hexanumeric codes to countries far away from each other as there were not enough combinations without using them twice or even more often.

however, during excellent conditions it might be possible in real life (but not theoretically ) to catch both nations at a time

Hrvatski radio is rather rare catch over here on the mainland. That will definitely take strongest E-Skip. had it many years ago in Bruges on 87.7 with very good signal. but no way in 2018 due to the lousy condx. HR signals need POWER over here.